21.6 litres that's... Oh boy, I always have trouble remembering my conversions - 5.71 Gallons (Thanks, google!) It's hard to answer that question though, as it varies from person to person. Tank-wise, yes you can accommodate a few shrimp. It's your fish that may not like them. I recommend trying ghost shrimp before you splurge on cherries, amanos, etc and see how they do. They're 6 for a dollar at my LFS. Worst that happens is that you don't have to feed for a day... No big money down the drain.